The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
E-UTRAN evolved UTRAN (LTE)
FACH forward access channel
GERAN GSM-enhanced data rates for global evolution (EDGE)
GSM global system for mobile communications
LTE long term evolution
RAT radio access technology
RSRQ reference signal received quality
SI system information
SIB system information block
SINR signal to interference plus noise ratio
TDD time division duplex
UE user equipment
UTRAN universal terrestrial radio access network
Co-owned U.S. patent application Ser. No. 13/023,675 (published Aug. 9, 2012 as US Patent Publication 2012/0202480) concerns measuring inter-frequency and inter-RAT neighbor cells and describes that the UE's measurement occasions are used for different neighbor cells depending on whether the UE has good or marginal coverage with its serving cell. It describes a priority re-selection algorithm in the E-UTRAN system by which the network can prioritize measurements of either a frequency layer or a RAT over another, so as to more efficiently use the available measurement occasions depending on the strength of the serving cell. Basic coverage is more important when the serving cell is weak. Service, such as looking for hot spot coverage to enable additional or enhanced mobile services beyond simply cellular call coverage, is more important when signal strength from the serving cell is stronger and maintaining a basic connection with the serving cell is not reasonably in doubt over the near term. In the former instance the above co-owned application prioritizes a lower priority neighbor cell search to better assure an alternate cell for maintaining connectivity in case signal strength from its serving cell deteriorates further, whereas in the latter instance the UE can override the 3GPP Release 99 measurement purposes and use its measurement occasions to detect high priority RATs and/or inter-frequencies that might offer enhanced services such as the increased data rates available through the E-UTRAN system.
The above co-owned application used two different thresholds Sprioritysearch1 and Sprioritysearch2 against which the serving cell signal strength was compared. If the received power and quality of the serving cell goes below either then the UE needs to perform a search on the GERAN and UTRAN RATs meeting the specified performance requirements. If the strength and quality of the serving cell is above both thresholds then the UE is not required to measure the lower priority RATs, and hence what was in the prior art as “spare” measurement occasions are instead used to measure the higher priority LTE RAT. This enables the UE to switch between coverage or service based measurements depending on the quality of the serving cell.
The 3GPP organization is now exploring measurements and reselections for a UE in the CELL_FACH state to the E-UTRAN (LTE) system. See for example document RP-110913 entitled WID UPDATE TO FURTHER ENHANCEMENTS OF CELL_FACH by Renesas Mobile Europe, TeliaSonera, Ericsson and ST-Ericsson (3GPP TSG-RAN Meeting #52; Bratislava, Slovakia; 31 May to 3 Jun., 2011) and RP-111321 entitled UPDATED WID: FURTHER ENHANCEMENTS TO CELL_FACH by Renesas Mobile Europe, TeliaSonera, Ericsson and ST-Ericsson (3GPP TSG-RAN Meeting #53; Fukukoa, Japan; 13 Sep. to 16 Sep., 2011). If one extends this principle to GERAN and UTRAN also, there would need to be a search in the various different RATs to maintain basic coverage for the UE.
The invention of the co-owned application above can be implemented so as not to impact the conventional performance for search and measurement of GERAN and UTRAN RATs. To extend that so that E-UTRAN is included in the low priority coverage search is not so straightforward because there are multiple frequency layers in GERAN, UTRAN and E-UTRAN which means that performing measurements on E-UTRAN may compromise the performance of GERAN and UTRAN measurements, similar to the 30% degradation the background section of that co-owned application details.